There have recently been active approaches to sustaining and protecting the environment all over the world, leading to increasing introduction of natural energy power generation devices using natural energy, such as wind power generation and solar power generation. Power generated by the natural energy power generation device is likely to undergo frequency fluctuations and voltage fluctuations depending on the weather or the like, and thus may cause trouble to a power system.
As one of the countermeasures against such a problem, there has been proposed a technology to suppress (absorb) the voltage fluctuations and the like by installing an electric storage device in addition to the natural energy power generation device, and thus to stably supply power to the power system. Note that, as the electric storage device described above, there has been known one including a lithium ion storage battery (secondary battery) having high capacity and high output characteristics.
Incidentally, the lithium ion storage battery may suffer performance degradation due to deposition of lithium metal on a negative electrode, when charged in a low-temperature environment or charged with a large current. Therefore, there has heretofore been known a charge control technology to safely perform charge by suppressing deposition of lithium metal.
For example, Patent Literature 1 discloses a charge control device including a negative electrode closed-circuit potential calculation unit configured to calculate a closed-circuit potential of a negative electrode using an open-circuit voltage acquired by an open-circuit voltage acquisition unit; a closed-circuit potential determination unit configured to determine whether or not the calculated negative electrode closed-circuit potential is less than a predetermined threshold; and a charging current control unit configured to reduce a charging current value when the negative electrode closed-circuit potential is less than the threshold.